The isolation of hepatitis B surface antigen (HBsAg) from positive plasma or serum by ultracentrifugation, column chromatography, etc., is known. When ultracentrifugation is used, the small size of the HBsAg particle (about 20 nm) requires about 18 hours per batch for the centrifugation step. Due to this time requirement, centrifugation becomes the limiting step in producing HBsAg.